Revisiting the iron-rich “ordinary Portland cement” towards valorisation of wastes: study of Fe-to-Al ratio on the clinker production and the hydration reaction

Ordinary Portland cement (OPC) is a strong and durable material with a well-established composition defined by national and regional standards. The required chemistry limits the amount of iron-rich materials that can be used as a feedstock. The work described in this paper investigates how substitution of iron for aluminium affects OPC clinker production. Herein, it was studied how this substitution affected clinker phase assemblage during the firing process, the paste hydration kinetics and products as well as the mechanical properties of the mortars. Results suggested that Fe to Al replacement did not affect substantially the melt formation at usual production temperatures. The formation of alite and ferrite were promoted, diminishing the formation of aluminate and belite. Regarding the hydration process it was obtained portlandite, ettringite, AFm and hydrogarnet as well as amorphous phase. Additionally, the Fe-rich cements presented longer setting times and slightly lower mechanical strength. These results are a first approach in the study of OPC clinkers with Fe-rich content and additional research provided in the future can enable the use of larger amounts of Fe-rich materials and residues in the OPC raw meal.